APPLICATIONS

Background: IRAP (also known as LNPEP) was originally described as an insulin-responsive aminopeptidase found in Glut4-containing vesicles (1). It is essentially always in the same compartments as Glut4 and has identical insulin-stimulated translocation patterns as Glut4 (2). IRAP is therefore considered to be a surrogate marker for Glut4 (2). IRAP was later found to be a critical enzyme that regulates the expression and activity of several essential hormones and regulatory proteins, including the Glut4 transporter (3,4). This membrane associated, zinc-dependent cystinyl aminopeptidase acts as both a receptor for angiotensin IV as well as the enzyme that catalyzes the synthesis of this essential hormone from its angiotensinogen precursor (5). IRAP catalyzes the hydrolysis of several peptide hormones, including oxytocin and vasopressin (4). Abnormal IRAP expression or activity is associated with several forms of cancer in humans, including renal and endometrial cancers (6,7).

APPLICATIONS

Background: IRAP (also known as LNPEP) was originally described as an insulin-responsive aminopeptidase found in Glut4-containing vesicles (1). It is essentially always in the same compartments as Glut4 and has identical insulin-stimulated translocation patterns as Glut4 (2). IRAP is therefore considered to be a surrogate marker for Glut4 (2). IRAP was later found to be a critical enzyme that regulates the expression and activity of several essential hormones and regulatory proteins, including the Glut4 transporter (3,4). This membrane associated, zinc-dependent cystinyl aminopeptidase acts as both a receptor for angiotensin IV as well as the enzyme that catalyzes the synthesis of this essential hormone from its angiotensinogen precursor (5). IRAP catalyzes the hydrolysis of several peptide hormones, including oxytocin and vasopressin (4). Abnormal IRAP expression or activity is associated with several forms of cancer in humans, including renal and endometrial cancers (6,7).

APPLICATIONS

Background: Aminopeptidase N (APN, CD13) is a widely expressed, membrane-bound proteolytic enzyme that breaks down peptides during digestion, cleaves cell surface antigens during antigen presentation, and acts as a receptor for human viruses, including several coronaviruses. This multifunctional protein is implicated in the regulation of many biological processes, including angiogenesis, cell proliferation, cell migration, inflammation and immune response (1,2). APN was originally identified as the cell surface antigen CD13, which is expressed in myeloid lineage hematopoietic cells and myeloid leukemia (3). Identified substrates of aminopeptidase N include the angiotensin I-III peptide hormones, the opioid peptide met-enkephalin, and cytokines MCP-1 and MIP-1 (4). Abnormal APN protein expression is seen in various forms of cancer, with high APN expression associated with poor survival in colon cancer and non-small cell lung cancer and silenced APN expression related to poor prognosis in prostate cancer (5-7).